Coupling arrangement



Nov. 9, 1937.

E. KLOTZ ET AL 8, 93

COUPLING ARRANGEMENT Original Filed May 14, 1932 2 Sheets-Sheet 1 To NEXT A E 1 STAGE p F"; l 1' SOURCE OF C t- 5'; SIGNAL ENE RGY INVENTORE ERNST KLOTZ Lmcryz LER Nov. 9, 1937.

E. KLOTZ ET AL COUPLING ARRANGEMENT Original Filed May 14, 1932 2 Sheets-Sheet 2 LU U 2 DJ O Bi 2 IT' .13 m

Jl II I SOURCE I 0F L g TO SIGNAL c- N v NEXT ENERGY 1 l '1 55 STAGE 9 2 5 1 3 O. 2 v L v INVENTOR ERNST KLOTZ ERICH ZEPLER ATT'oRNEY Patented Nov. 9, 1937 UNiTED STATES asses 2,098,393 COUPLING ARRANGEMENT Ernst Klotz and Erich Zepler, Berlin, Germany,

assigncrs to Telefunken Gesellschaft fiir Drahtlose Telegraphic m. b. 11., Berlin, Germany,a corporation of Germany Application May 14, 1932, Serial No. 611,259. Re-

newed August 1'7, 1.934. In Germany July 2,

9 Claims.

The present invention relates to amplifier coupling arrangements, and particularly to an arrangement for the transfer of radio frequency energy with interposition of a markedly detuned circuit between the energy source and the tuning circuit.

In the art of radio wave reception, circuits are often utilized for the transfer or feeding of radio frequency energy whose wavelength is markedly out of tune compared with the incoming wave. These circuits are usually in inductive, or capacitive, relationship with additional circuits which in turn are tuned to the incoming wave.

Figs. 1 2 show conventional circuits embodying the problem sought to be solved by the invention,

Fig. 3 shows a circuit embodying the invention,

Figs. 4 and 5 graphically show the operation of the circuit in Fig. 3.

Referring to Fig. 1, A is the antenna circuit which is detuned to the incoming wave and which is inductively coupled with the first tuned circuit E of the receiver. Fig. 2 shows a standard radio frequency amplifier stage comprising a screen grid tube S. In order that the gain throughout the incoming wave range may be as uniform as feasible it is customary to choose the natural wave length of the plate circuit P higher than the waves inside the incoming band to which the circuit Q is tuned, while to the inductive coupling is added a capacitive coupling in order that no loss in gain may occur for the long waves inside the receiving range. Now, one disadvantage of such 5 schemes is that the resonance curves of the receiver present peaks which are due to the tuning of the antenna, or plate, circuits, and the result is that powerful interfering stations will become discernible on these waves.

According to the invention the antenna, or plate, circuits in a circuit scheme as stated are artificially damped to such a marked point that the said resonance peaks will be unable to arise. The adoption of this remedy is an outcome of the proper appreciation of the fact that it is feasible, by choosing a suitable coupling between the detuned (untuned) and the tuned circuits and by choosing proper values for the artificial damping, to eliminate imperfections or trouble in resonance without appreciably impairing the amplification of the incoming waves.

As an example there may be cited here the data chosen in one instance and which has been checked up by actual measurements: 55

Wave band 200 to 600 meters Plate-circuit wave length 900 meters Coupling between plate and tuned circuit percent 69 Damping of antenna, for 900 meters 50 percent.

The coils of the untuned circuit, for example, may be wound of resistor wire of suitable proportions.

Fig. 5 shows the amplification characteristics that may be obtained from Fig. 3. Curve l of Fig. 5 is what is obtained if L is so large that the natural period of circuit LC lies far below the range of signals to be received. Curve 2 of Fig. 5 shows what happens if the natural period of circuit LC comes very close to the low frequency limit of the signal range. It is seen that the approaching resonance of circuit LC causes a big increase in amplification for the lowest signal frequency. If the natural frequency of LC is kept below by a sufiicient but not too great amount we get a fairly flat amplification curve such as curve 3 of Fig. 5.

Fig. 3 is a circuit having more than one degree of freedom or natural frequency. Thus, while the best amplification is obtained at the frequency of the tuned circuit NV, there may be also a noticeable amplification at the natural frequency of CL. If strong interfering signals occur at this frequency they may be transmitted through the system and cause noticeable interference. Fig. 4, the solid curve, shows how the impedance rises to a very high peak value at the natural period determined by L and its associated capacities. This high impedance is responsible for the amplification of the undesired interfering frequency referred to above. This diificulty is overcome according-to the present invention by the insertion of R which reduces the peak shown'in Fig. 4 to the small value shown by the dotted line.

t will be noticed that this dotted line does not differ appreciably from the solid line at frequencies in the signal range, and therefore, the system works substantially the same for signal frequencies whether R is present or not. Of course. R must not be made so great as to eliminate resonance at the low frequency entirely or else the flat amplification characteristic desired for the signals will not be obtained. The resistance R of the coil L should be made as large as is possible Without spoiling the uniformity of amplification of signal frequency. In practice it is preferable to obtain the desired value of resistance by winding the choke of sufliciently fine Wire, or if necessary of Wire having greater resistivity than copper, rather than to insert a separate resisto as shown in Fig. 3.

While we have indicated and described several systems for carrying our invention into effect, it will be apparent to one skilled in'the art that our invention is by no means limitedto the particular organizations shown and described, but that many modifications may be made without departing from the scope of our invention as set forth in the appended claims.

What-:we claim is: r V

1. An ,amplifyingsystem including a circuit tuned to signal frequency and an inductance coupled to said tuned circuit, said inductance together with its associated capacities determining a natural frequency less than, but not greatly less than, the lowest frequency to which said tunable circuit may be tuned, the value of the coupling between saidinductance and tuned circuit being of the order of twenty percent, and means for increasing the resistance of said inductance sufficiently to make the power factor of said inductance too poor to permit of sharp resonance effects at the said lower frequency.

2. A coupling network, for a radio frequency transmission circuit, comprising a source of radio frequency energy, a tunable-circuit, including a coilv and a variable condenser, adapted to be tuned over a range of radio frequencies, a second coil, connected to said source, coupledto said tunable circuit, ,the value of said coupling being at least twenty percent, said second coil and its associated capacitieshaving a natural resonance at a frequency less than, but notgreatly less than, the lowest frequency of said range, and said second coil being wound of sufficiently fine wire to increase the resistance of the second coil to a magnitude such that sharp, resonance effects at said natural resonancefrequency are prevented.

3. In combination with an amplifier tube, a tunable circuit connected between the input electrodes of the tube, said circuit including a variable condenser for tuning it over a range of wave lengths between 200and 600 meters, a'source of signal energy to be amplified, a coupling network between said source and tunable circuit,

said network including a coil which with its associated capacities has a natural period above, but not greatly above, the high end of said range, means for capacitatively coupling said coil and tunable circuit, said network including sufiicient resistance to make the power factor of said coil too poor to permit'of sharp resonance effects at said natural period.

4. In combination withan. amplifier tube, a tunable circuit connected between the input electrodes of the tube, said circuit including avariable condenser for tuning it over a range of wave lengths between 200 and '600 meters, a source of signal energy to be-amplified, a coupling network betweensaid source and tunable circuit, saidnetwork including a coil-which with its associated capacities has a natural period above, but not greatly above, the high end of said range and at about 900 meters, means for capacitatively coupling said coiland tunable circuit, said network including-sufiicient resistance to make the power factor of said coil too poor to permit of sharp resonance effects'at said natural period.

5. In combination with an amplifier tube, a tunable circuit'connected between the input'eleotrodes of the tube, said circuit includinga variable condenser for tuning it over a range of wave lengths between 200 and 600 meters, a source of signal 'energy to be amplified, acoupling network between said source and tunable circuit, said network including-a coil which with its associated capacities has a natural period above, but. not greatlyaabove, the high end of said range, means for capacitatively coupling said coil and tunable circuit so that the coupling is g at least twenty per cent, said network including sufficient resistance to make the power factor of tunable circuit connected between the input electrodes of the tube, said circuit including a variable condenser for tuning it over a range of wave lengths between 200 and 600 meters, a source of signalenergy to be amplified, a coupling network between said source and tunable circuit, said network including a coil which with its associated capacities has a natural period above, but not greatly above, the high end of said range, means for capacitatively coupling said coil and tunable circuit, said network including sufiicient resistance, provided in the windings of said coil, to make the power factor of said coil too poor to permit of sharp resonance effects at said natural period.

7. In combination with an amplifier tube, a tunable circuit connected between the input electrodes of the tube, said circuit including a variable condenser for tuning. it over a range of wave lengths between 200 and 600 meters,-a source of signal energy to be amplified, a coupling net- 7 work between said source and tunable circuit,

said network including a coil which with its associated capacities has a'natural period above, but not greatly above, the high end of said range and at about 900 meters, means for capacitatively coupling. said coil and tunable circuit so that the coupling is at least twenty percent, said network including sufficient resistance, provided in the windings of said coil, to make the power factor of said coil too poor to permit of sharp resonance effects. at said natural period.

8. An amplifying system including a circuit tuned toa signal frequency and a single inductor of high inductance coupled to said tuned circuit, thevalue of the coupling between said inductor and the tuned circuit being of the orderof 20%, and means for increasing the resistance of said inductor sufliciently to make the power factory thereof too poor to permit of sharp resonance effects at the natural period of the inductor.

9. A coupling network for a radio frequency transmission circuit which includes an amplifier tube having its input electrodes coupled to a source of signal energy, a second amplifier tube following the first tube and having a tunable ciri cuit, including a coil and a variable condenser, connected between, its input electrodes, a second'coil connected between the output electrodes ofrthefirst amplifier tube, said second coil having a substantially, high inductance and having a predetermined coil period, said second coil and the tuned circuit having a coupling of the order of 20%, and said second coil being wound of sufilciently fine wire toincrease the resistance thereof to a magnitude such that sharpresonance effects at the said natural period are prevented.

ERICH ZEPLER. ERNST KLOTZ. 

